Compression implants of this class are used in surgical medicine, especially in operations for restoring the normal functions of pathologic or injury-related damage to the spinal column.
Curvatures of the spine may be the consequence of, e.g., disturbances of growth, which lead to wedge-shaped changes in the spinal column, or they may be due to tuberculous collapse of individual vertebral bodies. Vitamin D deficiency has also been known to be able to lead to severe rachitic curvatures of the spine, and calcipenia has been known to be able to cause collapse of vertebrae after the menopause. In addition, accident-related vertebral fractures, which must be treated surgically, occur with increasing frequency.
To correct such postural defects or to stabilize these disease-related or traumatic vertebral fractures, individual vertebrae or vertebral prostheses are mutually braced, clamped, or fixed to or with one another in practice. Metal wires have hitherto been used for this purpose in order to stabilize the vertebrae affected or to attach the aforementioned vertebral prostheses to the vertebrae.
Screw clamps, whose jaws can be pushed over two or more vertebrae during the operation and which can be contracted with a conventional set screw, e.g., in the manner of pipe clamps or the like, have been known as well. These jaws have a hook-shaped design. While one jaw is provided with a smooth bore for passing through the screw shaft, the second jaw has a bore provided with internal threads, into which the screw can be screwed in order to move the two jaws toward one another, and the screw head is located on the outside at the edge of the smooth bore.
These prior-art clamps are unsatisfactory for several reasons. First of all, it is impossible for a single surgeon to insert such a clamp. In addition, its manipulation is very complicated and, in particular, it requires a large surgical incision opening to permit insertion of such a clamp, because the screw head, which is arranged at one end of the screw to which the rotating tool, e.g., a 90.degree. offset screw driver, must be attached. In addition, the two jaws, must be held individually during rotation, as long as screwing in of the screw is taking place, in order to prevent them from leaving the position required for their proper function. Due to the relatively long span distance and the simple, self-locking thread, a very great number of rotations of the screw are also necessary in order to bring the two jaws to the intended final distance needed for proper function.